Several methods are known for treating articles or materials by particle blasting using particles of a material that can change its physical state, for instance ice or solid carbon dioxide. See for instance DK Pat. No. 92.884, Swedish published specification with the publication No. 413.380, GB Pat. No. 1,397,102, GB Patent Application No. 2,095, 538 and U.S. Pat. No. 3,676,963.
The above-mentioned specifications contain only a brief mention of how it is contemplated that the ice particles in question could be produced. Processes referred to comprise either crushing followed by screening, peeling off or scraping, possibly with subsequent grinding, or condensation or freezing in a cooling fluid. It is obvious that by producing ice particles in the ways thus indicated, control of the final form of the particles will be quite poor. Granted, the SE published specification No. 413,380 mentions certain desired characteristics of the finished particles, but the specification does not state anything concrete as to how the particles are to be produced. Further, said publication refers to particles of sublimable substance, for instance solid carbon dioxide or "carbon dioxide snow", which can only be formed by compression of particles smaller than the desired finished particles.